Makefile: validate generated files as part of build

For example...

$ make
GEN checkpkg
GEN commitpkg
GEN archco
archco: line 179: unexpected EOF while looking for matching `"'
archco: line 181: syntax error: unexpected end of file
make: *** [archco] Error 2

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Signed-off-by: Pierre Schmitz <pierre@archlinux.de>

Makefile

@@ -77,6 +77,7 @@ edit = sed -e "s|@pkgdatadir[@]|$(DESTDIR)$(PREFIX)/share/devtools|g"
 	@m4 -P $@.in | $(edit) >$@
 	@chmod a-w "$@"
 	@chmod +x "$@"
+	@bash -O extglob -n "$@"
 
 clean:
 	rm -f $(BINPROGS) bash_completion zsh_completion